Each of these functions returns a file descriptor for the opened file.

If filename or oflag is a NULL pointer, or if oflag or shflag is not within a valid range of values, the invalid parameter handler is invoked, as described in Parameter Validation. If execution is allowed to continue, these functions return -1 and set errno to one of the following values.

EACCES

The given path is a directory, or the file is read-only, but an open-for-writing operation was attempted.

EEXIST

_O_CREAT and _O_EXCL flags were specified, but filename already exists.

The _sopen function opens the file specified by filename and prepares the file for shared reading or writing, as defined by oflag and shflag. _wsopen is a wide-character version of _sopen; the filename argument to _wsopen is a wide-character string. _wsopen and _sopen behave identically otherwise.

Generic-Text Routine Mappings

Tchar.h routine

_UNICODE and _MBCS not defined

_MBCS defined

_UNICODE defined

_tsopen

_sopen

_sopen

_wsopen

The integer expression oflag is formed by combining one or more of the following manifest constants, which are defined in <fcntl.h>. When two or more constants form the argument oflag, they are combined with the bitwise-OR operator ( | ).

_O_APPEND

Repositions a file pointer to the end of the file before every write operation.

_O_BINARY

Opens a file in binary (untranslated) mode. (See fopen for a description of binary mode.)

_O_CREAT

Creates a file and opens it for writing. Has no effect if the file specified by filename exists. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_SHORT_LIVED

Creates a file as temporary and if possible does not flush to disk. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_TEMPORARY

Creates a file as temporary; the file is deleted when the last file descriptor is closed. The pmode argument is required when _O_CREAT is specified.

_O_CREAT | _O_EXCL

Returns an error value if a file specified by filename exists. Applies only when used with _O_CREAT.

_O_NOINHERIT

Prevents creation of a shared file descriptor.

_O_RANDOM

Specifies primarily random access from disk.

_O_RDONLY

Opens a file for reading only. Cannot be specified with _O_RDWR or _O_WRONLY.

_O_RDWR

Opens a file for both reading and writing. Cannot be specified with _O_RDONLY or _O_WRONLY.

Opens a file and truncates it to zero length; the file must have write permission. Cannot be specified with _O_RDONLY. _O_TRUNC used with _O_CREAT opens an existing file or creates a file.

Note

The _O_TRUNC flag destroys the contents of the specified file.

_O_WRONLY

Opens a file for writing only. Cannot be specified with _O_RDONLY or _O_RDWR.

_O_U16TEXT

Opens a file in Unicode UTF-16 mode.

_O_U8TEXT

Opens a file in Unicode UTF-8 mode.

_O_WTEXT

Opens a file in Unicode mode.

To specify the file access mode, you must specify either _O_RDONLY, _O_RDWR, or _O_WRONLY. There is no default value for the access mode.

When a file is opened in Unicode mode by using _O_WTEXT, _O_U8TEXT, or _O_U16TEXT, input functions translate the data that's read from the file into UTF-16 data stored as type wchar_t. Functions that write to a file opened in Unicode mode expect buffers that contain UTF-16 data stored as type wchar_t. If the file is encoded as UTF-8, then UTF-16 data is translated into UTF-8 when it is written, and the file's UTF-8-encoded content is translated into UTF-16 when it is read. An attempt to read or write an odd number of bytes in Unicode mode causes a parameter validation error. To read or write data that's stored in your program as UTF-8, use a text or binary file mode instead of a Unicode mode. You are responsible for any required encoding translation.

If _sopen is called with _O_WRONLY | _O_APPEND (append mode) and _O_WTEXT, _O_U16TEXT, or _O_U8TEXT, it first tries to open the file for reading and writing, read the BOM, then reopen it for writing only. If opening the file for reading and writing fails, it opens the file for writing only and uses the default value for the Unicode mode setting.

The argument shflag is a constant expression consisting of one of the following manifest constants, which are defined in <share.h>.

_SH_DENYRW

Denies read and write access to a file.

_SH_DENYWR

Denies write access to a file.

_SH_DENYRD

Denies read access to a file.

_SH_DENYNO

Permits read and write access.

The pmode argument is required only when _O_CREAT is specified. If the file does not exist, pmode specifies the file's permission settings, which are set when the new file is closed the first time. Otherwise, pmode is ignored. pmode is an integer expression that contains one or both of the manifest constants _S_IWRITE and _S_IREAD, which are defined in <sys\stat.h>. When both constants are given, they are combined with the bitwise-OR operator. The meaning of pmode is as follows.

_S_IWRITE

Writing permitted.

_S_IREAD

Reading permitted.

_S_IREAD | _S_IWRITE

Reading and writing permitted.

If write permission is not given, the file is read-only. In the Windows operating system, all files are readable; it is not possible to give write-only permission. Therefore, the modes _S_IWRITE and _S_IREAD | _S_IWRITE are equivalent.

_sopen applies the current file-permission mask to pmode before the permissions are set. (See _umask.)